1. Field of the Invention
This invention relates to oil rings and oil-ring guide systems and more particularly to a novel and highly effective oil ring and oil-ring guide system for sleeve bearings.
2. Description of the Prior Art
A major determinant of the useful life of rotating machinery such as electric motors and generators is the effectiveness with which the machine bearings are lubricated. Any rotating machine such as an electric motor or generator has a stationary part and a rotating part. In an electric motor or generator, these parts, or at least the portions thereof that generate the electromagnetic fields, are respectively called the "stator" and the "rotor." The rotor rotates on a shaft, and the shaft is supported by sleeve bearings that are stationary with respect to the stator.
Friction is generated in the sleeve bearings during operation of the machine, and measures must be adopted to minimize the friction if the bearings are not to wear out prematurely. The need to minimize friction becomes greater the greater the size and power of the machine, both because, other factors being equal, more friction is generated by a large, powerful machine and because the cost of a large, powerful machine makes it all the more important to maximize its useful life.
In electric motors and generators that are "large," for example that generate from several horsepower to ten thousand horsepower or more, it is customary to employ oil rings to help to lubricate and cool the sleeve bearings. An oil ring is an annulus that is received within a slot formed in the bearing bushing, encircles and rides on the shaft, and dips into an oil reservoir mounted below the bearing bushing. Rotation of the shaft causes rotation of the oil ring in the same direction so that the oil ring carries oil from the reservoir into the bearing for lubrication thereof.
A problem associated with the operation of conventional oil rings is that they do not deliver as much oil to the bearing as is required for optimum lubrication of the bearing during operation of the machine. By the nature of its construction, the oil ring cannot be geared to the rotor shaft, and the oil ring rotates in the direction of shaft rotation only because the oil ring rides on the shaft and a certain friction develops as the shaft rotates.
However, friction is also developed between the oil ring as it rotates and the walls of the slot in which the oil ring is received. These walls must be fairly close to the oil ring in order to guide it properly and prevent it from wandering in the axial direction of the shaft. The walls of the slot inevitably have a certain roughness. The degree of roughness can be minimized by spending a great deal of money on machining, but regardless of how carefully the walls are machined, they will exhibit some imperfections. Moreover, the walls extend over a considerable fraction of the circumference of the oil rings, as compared to the footprint or area of contact between the oil rings and the shaft. The latter footprint is very small, since the radius of curvature of the shaft is less than that of the oil rings. In addition, the oil bridges the stationary and moving surfaces and itself produces drag tending to slow the rotation of the oil ring.
As a result of the friction between the oil ring and the walls of the slot in the sleeve bearing in which the oil ring is received, plus the drag caused by the oil itself, and because the inner diameter of the oil ring exceeds the outer diameter of the shaft, the rotational speed of the oil ring is very much lower than the rotational speed of the shaft. For example, in the case of a shaft running at 3600 rpm, a conventional oil ring will rotate at about 120 rpm.
A rotational speed of the oil ring of 120 rpm is sufficient to provide a good deal of lubrication to the sleeve bearing, but not as much as is required in order to maximize the life of the bearing. To achieve maximum bearing life, it would be necessary to increase the rotational speed of the oil ring by a substantial factor. This cannot easily be done because of the lack of gearing between the oil ring and the shaft and, of course, because of the presence of oil on the oil ring and shaft, which renders the coefficient of friction between the oil ring and shaft very low so that the oil ring easily slips on the shaft.